1. Field of the Invention
The present invention is directed to a device for generating radiant energy. More particularly, the present invention is directed to a device for generating radiant energy emitted by a rare earth metal oxide or rare earth metal halide in electrical communication with, and disposed between, a first and second electrode.
2. Description of the Prior Art
The development of light emitting devices is a major activity in the semiconductor arts. This is to be expected insofar as information propagation by means of harnessing light waves so generated represents a potential source of information transmission. Transmission by light waves removes speed and power restrictions associated with electrical wire transmission. Thus, the development of efficient light emitting semiconductor structures represents an attractive and burgeoning area of technical development.
Currently, the most efficient light-emitting semiconductor materials are direct-gap compound semiconductors e.g. III-V and II-VI materials.
However, severe processing constraints associated with these materials have prevented the development of very large scale integrated (VLSI) circuits utilizing these materials. Thus, attention has been directed to modifications of silicon-based semiconductors insofar as silicon semiconductors are the best developed and understood semiconductor materials. Unfortunately, silicon is an indirect bandgap semiconductor. As such, it exhibits extremely poor luminescence, whether electrically-pumped or optically-pumped.
In view of the above remarks recent research has focused on the manufacture of optoelectronic integrated circuits (OEICs) on silicon. This research has attempted to develop chip-to-chip interconnects, parallel processing and the integration of photonics on silicon chips. The integration of photonics on silicon chips require operation of a silicon-based light source at 1.54 microns. That wavelength corresponds to an absorption minimum in silica-based optical fibers. This, in turn, has focused upon the utilization of erbium-doped silica fiber amplifiers.
This latter development is the result of the fact that erbium atoms have a strong absorption band centered around 0.98 microns, corresponding to a .sup.4 I.sub.15/2 to .sup.4 I.sub.11/2 (4f.sup.11) transition and a strong emission spectrum centered around 1.54 microns, corresponding to a .sup.4 I.sub.13/2 to .sup.4 I.sub.15/2 (4f.sup.11) inner atomic transition. When Er-doped silica fiber is photopumped by semiconductor lasers emitting at 0.98 microns, the gain spectrum peaks around 1.54 microns. Thus, an optical signal, centered around 1.54 microns, passing through an Er-doped silica photopumped fiber would be greatly amplified. In fact, if sufficient population inversion were obtained, and a Fabry-Perot cavity created, an Er-doped fiber laser would be obtained.
In view of these scientific facts much activity has focused upon doping of silicon with erbium to effectuate the aforementioned results. Franzo et al., Applied Physics Letters, 64, 2235, (1994) and Michel et al. Applied Physics Letters, 64, 2842 (1994) describe ion implantation of erbium into silicon. Serna et al., J. ADpl. Phys., 75, 2644 (1994) sets forth Er incorporation during molecular beam epitoxy growth. Michel et al., J. A)pl. Phys., 70, 2672 (1991) describes the coimplantation of oxygen, carbon, nitrogen and fluorine with erbium into silicon.
Surprisingly, these studies emphasize that luminescence intensity depends strongly on the concentration of other impurities. Indeed, these studies indicate that the presence of oxygen is imperative for light emission with acceptable quantum efficiency. Alder et al. Appl. Phys. Letters, 61, 2180 (1992) found that extended X-ray absorption fine-structure (EXAFS) measurements from erbium implanted by the Czochralski (CZ) method and by the float-zone (FZ) technique produce dramatically different local structures around Er with respect to coordination number, type of atom and bond length. These studies show that the first coordination shell in Er: FZ Si closely resemble the 12 Si atoms in ErSi.sub.2, whereas the first shell around Er in the CZ technique resembles the 6 oxygen atoms in Er.sub.2 O.sub.3. This explains how the local chemical environment around Er determines its optical activity, i.e. Er in Si effectively acts as a microscopic getter, reacting in with Si only when either the amount of or accessability to oxygen is limited. Since the sixfold oxygen coordination to erbium cannot be centrosymmetric, the crystal field of the Si host lattice breaks inversion symmetry and mixes states of opposite parity, allowing the .sup.4 I.sub.13/2 to .sup.4 I.sub.15/2 transition (which is dipole forbidden in the free atom) to take place. Because the magnitude of the crystal-field splitting, which determines the transition probability, depends on the symmetry and chemical nature of the ligands bound to Er, the two different local environments in CZ and FZ lead to very different degrees of optical activity.
The prior art, i.e. Ennan, et al, Appl. Phys. Letters, 46, 381 (1985), reports photoluminescence and electroluminescence from Er-doped Si. the aforementioned Franzo et al. and Michel et al. Applied Physics Letters articles report the formation of light emitting diodes (LEDs) fabricated in silicon p.sup.+ -n.sup.+ diodes with Er and O co-doping at the metallurgical junction region. Kimura et al., Appl. Phys. Letters, 65, 983 (1994) reports electrochemical Er doping of porous Si and the room temperature luminescence of the so-doped silicon at 1.54 microns.
In spite of the above discussed activities, the introduction of erbium into silica has not produced the requisite quantum efficiency necessary to commercialize this advance. The above discussed scientific developments indicate that erbium-oxygen complexes are crucial to intra-shell luminescence. However, carrier transfer to these complexes from a host silicon lattice remains unsolved. Therefore, there is a continuing need in the art for further development of erbium and other rare earth metal modified silicon semiconductors to provide light-emitting devices.